Apparatus for electroplating metals on mirrors



Oct. 29, l 940.

P. R. MORRIS ET AL APPARATUS FOR ELECTROPLATING METALS 0N MIRRORS Filed'Jan. 15, 1937 2 Sheets-Sheet l "7"!) 51/5511. LINT/NE a;

IN VEN TORS F? R M01221;

6w 4 TTORNEYS.

29, 1940. P, R, MCRRls AL 2,219,695

APPARATUS FOR ELECTROPLATING METALS 0N MIRRORS Filed Jan. 15, 1937 2 Sheets-Sheet 2 10 I 18 P3 INVENTORS ATTORNEYS.

Patented Oct. 29, 1940 UNITED. STATES APPARATUS FOR ELECTROPLATING METALS ON MIRRORS Paul R. Morris and Elmer J Ballintine, Tarentum,

Pa., assignors to Pittsburgh Plate Glass Company, a corporation of Pennsylvania I Application January 15, 1937, Serial No.,120,'l26

3 Claims.

The invention relates to apparatus for electroplating the metallic reflecting coatings on mirrors. Ordinarily the reflecting coating is of silver, and the plating metal is copper, but it will be i understood that the invention is equally'applicable .to plating with metals other than copper, which are in the E. M; F. series above the reflecting..coating, and that the'reflecting coating may be of. gold, copper, or other metal. The invention hasfor one of its objects the provision of an improved process and apparatus which requires no source of extraneous current supply. Further objects are the provision of a process and apparatus characterized by simplicity of operation,

low initial and operating cost and without a requirement for meters or external controls. Still further objects are the provision of a process and apparatus (1) in which the plating can take place in a solution which is nearly neutral, thus 0 lessening the stripping tendency of the metal film; (2) in which the formation of'copper sludge in the plating solution is avoided; (3) in which the current may be maintained very uniform and regulated to meet requirements; and (4) which 5 results in the deposit of a metallic film whichis cleaner and brighter than that produced by methods heretofore commonly employed. Certain embodiments of the apparatus are illustrated in the accompanying drawings, wherein:.

0 Figure 1 is a perspective view, partially broken away, of the apparatus. Fig. 2 is an enlarged partial section through the apparatus. And Figs. 3 and 4 are partial sections through apparatus involving modifications.

Referring to Figs; -1 and 2, 5 is a large relatively flat container, carrying an electrolyte 8; I is-a container or tray of porous material, such as unglazed clay carrying an electrolyte 8; 9 is a plate of replacing metal carried by a support It of .0 rubber or the like; H, II, etc. are a series of posts of copper or other suitable conducting material resting on the plate 9 and supporting the tray 1; and I2 is a glass plate which is silvered on its lower side and rests upon the posts. The

5 posts are provided with insulating sleeves iii of rubber which cover the posts except at their extreme ends where they contact with the plate 9 and the silvering on the lower face of the glass I plate. The rubber sleeves are provided with flanges lyingabove and below the bottom of the tray 1, and fit the perforations through the tray bottom, so as to prevent a leakage of electrolyte from one container to the other.

I If the silver-film on the glass plate is to be plated with copper, the electrolyte 8 is preferably a solution of copper sulphate, a body of crystals being maintained in the bottom of the tray to keep the liquid at the saturation point. It a plating of some other metal were to be applied, the electrolyte would comprise a suitable salt of such other metal.

The container 5 is preferably of steel lined with rubber, and the electrolyte 6 is preferably a salt of the displacing metal 8, which in this instance is zinc. Zinc sulphate may be employed or one of the mineral acids, such as sulphuric acid. It is also feasible to substitute some other metal for the zinc lying higher in the E. M, F. series than the plating metal, such as iron or aluminum. In order to prevent local galvanic couples incident to impurities in the zinc plate, such plate is preferably amalgamated.

Inoperation, the posts ll act as electrical connections between the coating on the plate I! and the zinc plate, current fiow being downward. Both electrolytes undergo partial dissociation and the copper ions in the electrolyte 8 travel toward the silver film and form a copper plating thereon. The zinc ions from the electrolyte 6 also travel toward the silver film, but do not reach it, as the zinc, passing through the pores of the tray, unite with the sulphate ions left by the breaking down of the copper sulphate, so that zinc sulphate is formed. The porous cup allows the ions to pass through its pores, but prevents the rapid admixture of the two electrolytes. When a plating of copper of the desired thickness has been deposited on the silver film, the plate is removed and another one is substituted.

In the apparatus of Fig. 3, the posts ll of the apparatus of Figs. 1 and 2 are dispensed with, and electrical connections from the zinc plate 5 and the silver film on the lower side of the glass plate l2 are provided in the form of the posts ll which carry at their upper ends the bronze springs l5. The posts are carried in rubber casings I6 which hook over the edge of the container 5 and rest on the bottom thereof. The' side of the casings are slotted, so that the edge of the plate 9 of displacing metal, will fit therein and make contact with the posts. The springs are bolted to the upper ends of the posts, and normally lie above the surface of the electrolyte, as shown in dotted lines. When the glass plate is placed on the springs, they are depressed to the full line position where they are stopped by the blocks I! of insulating material resting on the bottom of the tray. The springs are sheathed in rubber except at their free ends which contact Y with the silver coating on the lower side of the sary electrical contacts uponthe metal in the tray comprising a salt glass plate. The zinc plate 9 is supported by the casings [6 as heretofore mentioned and by other blocks in of insulating material as in the apparatus of Figs. 1 and 2. The tray 6 is supported on the zinc plate by the rubber blocks l8. The apparatus functions in the same manner as the other type of apparatus.

In the apparatus of Fig. 4, the glass plate I! shown as supported from above by means of a vacuum cup l9 carried by a frame 20 having legs resting upon the edge of the container 5. Electrical connections between the sliver film on the plate l2 and the zinc plate 9 are, provided in the form of insulated wires 2| having spring metal clips 22 and 23 at their ends which grip the plates I2 and 9 respectively and make the neceswith the silver film and the zinc.

The apparatus, as described, will provide constant current which may be varied by the soluti'on used, thedistance of the displacing metal from the surface of disposition and by the porosity of the tray 1. The apparatus. is easy to operate and of low initial cost requiring no generators, meters, or external controllers. No copper sludge is formed in the plating solution as is the case with plating systems heretofore used, and the deposited film is cleaner and brighter than those produced by the methods heretofore commonly employed. Other advantages will be readily apparent to those skilled in the art.

- What we claim is:

1. An apparatus for electroplating the metallic reflecting coating of a glass plate, com-' prising a container, a plate of displacing metal supported in the container in horizontal position above the bottomthereof, a tray of porous material seated in the container and supported plate, electrical conducting means for supporting the glass plate to be plated in horizontal position with its coated face down and contacting with said conducting means, an electrolyte in the container and in the tray, the one of the metal which v is to plate the metallic coating, and electrical connecting means short circuiting said conducting means and said plate of displacing metal.

2. An apparatus for electroplating the metallic reflecting coating of a glass plate, comprising a container, a plate of displacing metal supported in the container in horizontal position above the bottom thereof, a tray of porous material seated in the container, vertical metal posts extending through the bottom of the tray with their lower ends in engagement with the metal plate and acting as supports for the tray and with their upper ends at a common level and adapted to act as a 3 support for the glass plate which is to be plated,

sleeves of insulating material surrounding the posts except at the ends which contact with the plate of displacing metal and with the metallic coating on the lower side of the glass plate, shortcircuiting the metal plate and the metallic coating of the glass plate and an electrolyte in the container and in the tray, the one in the tray comprising a salt of the metal which is to plate the metallic coating.

3. An apparatus for electroplating the metallic reflecting coating of a glass plate comprising a tray of porous material, electrical conducting means for supporting the glass plate in a horizontal position in the tray with its coated face down and contactin with said means, a container inwhich the tray is seated, a body of displacing metal in the container, electrolytes in the tray and container, the one in the tray comprising a salt of the metal which is to plate the metallic coating, and electrical connecting means short circuiting said conducting means and the body of displacing metal, said conducting means comprising springs whose ends normally lie above the surface of the electrolyte but which are depressed by the weight of the glass plate and lie beneath such surface during the plating operation.

PAUL R. MORRIS. ELMER J. BALLINTINE. 

